Distribution and isotopic composition of n-alkanes from grass, reed and tree leaves along a latitudinal gradient in China

Abstract

Molecular composition and compound-specific carbon and hydrogen stable isotope ratios of n-alkanes are presented for leaves of grass, reeds and trees from five regions extending between latitudes 22° and 39°, China. The distribution of n-alkanes ranges from C₁₅ to C₃₅ with a high odd over even predominance and carbon-number maxima at C₂₇, C₂₉ or C₃₁. The carbon preference index (CPI) values are from 3.49 to 17.25, with mean values increasing following tree leaf > reed > grass. The average chain length (ACL) values are between 26.24 and 30.26 and the mean values increase following grass > reed > tree leaf. It is observed that C_max, CPI and ACL values of n-alkanes in plants from low latitudes are higher than those from high latitudes. The δ¹³C values of C₂₇ and C₂₉ n-alkanes in plants range from –25.3 to –35.5‰ and the grass has a lighter mean carbon isotopic composition than the reed and tree leaf. The δD values of C₂₇ and C₂₉ n-alkanes in the plants are between –132.1 and –192.6‰ and the mean hydrogen isotopic compositions of C₂₇ and C29 n-alkanes in the grass are lighter than those in the reed and tree leaves. C₂₇ and C₂₉ n-alkanes in the grass and tree leaves from high-latitude and elevation area have relatively lighter hydrogen isotopic composition, indicating that these δD values can be used as excellent indicators of environment and climate.